Petroleum refining – straight-run distillation In crude oil atmospheric/vacuum distillation (without cracking), what is a typical percentage yield of straight-run naphtha obtained directly from the crude?
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A6
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B18
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C12
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D2
Answer
Correct Answer: 12
Explanation
Introduction / Context:In refinery practice, the crude distillation unit (CDU) and, where used, the vacuum distillation unit (VDU) separate crude oil into straight-run fractions by boiling range without chemical conversion. One of the most important light products from straight-run fractionation is naphtha, which is later treated, reformed, or isomerised for gasoline blending and petrochemical use. Knowing a typical straight-run naphtha yield helps with rough material balances and exam questions about slate distribution.Given Data / Assumptions:
- Process: straight-run atmospheric/vacuum distillation only (no cracking or reforming).
- Desired: a typical percentage yield (by volume or weight trend) asked in exam style; choose the closest option.
- Feed: a representative medium crude; not a condensate-rich edge case.
Concept / Approach:Crude assays for common medium crudes often show straight-run naphtha in a low-to-mid teens percent range, while lighter condensates may give higher values and heavy/sour crudes somewhat lower. Exam keys typically anchor on a simple round figure near the middle of this typical band. Among the offered choices, 12 is a standard teaching value for straight-run naphtha yield from a representative crude slate.Step-by-Step Solution:
List plausible straight-run naphtha yields for medium crudes: roughly 10–20 percent.Compare with the options 2, 6, 12, 18.2 and 6 are too low for most medium crudes; 18 can occur for light/condensate crudes but is on the higher side for a typical exam assumption.Select the mid-range value 12 as the representative typical yield.Verification / Alternative check:Introductory refinery texts and crude assay tables commonly show straight-run naphtha of about 10–15 percent for medium crudes, aligning well with 12 as a round, memorable figure for examinations.
Why Other Options Are Wrong:
- 2: Unusually low; would indicate a very heavy crude or atypical cut definition.
- 6: Still lower than common medium-crude assays.
- 18: Possible for very light crudes/condensates but not representative of a typical “about” value.
Common Pitfalls:Confusing straight-run naphtha with total gasoline after conversion (reforming/FCC), which is higher. Also mixing weight vs volume percent does not change the ordering of options here.
Final Answer:12